/*-------------------------------------------------------------------------
 *
 * fastpath.c--
 *    routines to handle function requests from the frontend
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    $Header: /usr/local/cvsroot/postgres95/src/backend/tcop/fastpath.c,v 1.3 1996/11/08 05:59:26 momjian Exp $
 *
 * NOTES
 *    This cruft is the server side of PQfn.
 *
 *    - jolly 07/11/95:
 *
 *    no longer rely on return sizes provided by the frontend.  Always
 *    use the true lengths for the catalogs.  Assume that the frontend 
 *    has allocated enough space to handle the result value returned.
 *    
 *    trust that the user knows what he is doing with the args.  If the 
 *    sys catalog says it is a varlena, assume that the user is only sending
 *    down VARDATA and that the argsize is the VARSIZE.  If the arg is
 *    fixed len, assume that the argsize given by the user is correct.
 *  
 *    if the function returns by value, then only send 4 bytes value 
 *    back to the frontend.  If the return returns by reference, 
 *    send down only the data portion and set the return size appropriately.
 * 
 *   OLD COMMENTS FOLLOW
 *
 *    The VAR_LENGTH_{ARGS,RESULT} stuff is limited to MAX_STRING_LENGTH
 *    (see src/backend/tmp/fastpath.h) for no obvious reason.  Since its
 *    primary use (for us) is for Inversion path names, it should probably
 *    be increased to 256 (MAXPATHLEN for Inversion, hidden in pg_type
 *    as well as utils/adt/filename.c).
 *
 *    Quoth PMA on 08/15/93:
 *
 *    This code has been almost completely rewritten with an eye to
 *    keeping it as compatible as possible with the previous (broken)
 *    implementation.
 *
 *    The previous implementation would assume (1) that any value of
 *    length <= 4 bytes was passed-by-value, and that any other value
 *    was a struct varlena (by-reference).  There was NO way to pass a
 *    fixed-length by-reference argument (like char16) or a struct
 *    varlena of size <= 4 bytes.
 *	
 *    The new implementation checks the catalogs to determine whether
 *    a value is by-value (type "0" is null-delimited character string,
 *    as it is for, e.g., the parser).  The only other item obtained
 *    from the catalogs is whether or not the value should be placed in
 *    a struct varlena or not.  Otherwise, the size given by the
 *    frontend is assumed to be correct (probably a bad decision, but
 *    we do strange things in the name of compatibility).
 *
 *-------------------------------------------------------------------------
 */
#include <string.h>

#include "postgres.h"

#include "tcop/tcopdebug.h"

#include "utils/palloc.h"
#include "fmgr.h"
#include "utils/builtins.h"	/* for oideq */
#include "tcop/fastpath.h"
#include "libpq/libpq.h"

#include "access/xact.h"	/* for TransactionId/CommandId protos */

#include "utils/syscache.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_type.h"


/* ----------------
 *	SendFunctionResult
 * ----------------
 */
static void
SendFunctionResult(Oid fid,	/* function id */
		   char *retval, /* actual return value */
		   bool retbyval,
		   int retlen	/* the length according to the catalogs */
		   )
{
    pq_putnchar("V", 1);
    
    if (retlen != 0) { 
	pq_putnchar("G", 1);
	if (retbyval) {		/* by-value */
	    pq_putint(retlen, 4);
	    pq_putint((int)retval, retlen); 
	} else {		/* by-reference ... */
	    if (retlen < 0) {		/* ... varlena */
		pq_putint(VARSIZE(retval) - VARHDRSZ, 4);
		pq_putnchar(VARDATA(retval), VARSIZE(retval) - VARHDRSZ);
	    } else {			/* ... fixed */
		pq_putint(retlen, 4);
		pq_putnchar(retval, retlen);
	    }
	}
    }

    pq_putnchar("0", 1);
    pq_flush();
}

/*
 * This structure saves enough state so that one can avoid having to
 * do catalog lookups over and over again.  (Each RPC can require up
 * to MAXFMGRARGS+2 lookups, which is quite tedious.)
 *
 * The previous incarnation of this code just assumed that any argument
 * of size <= 4 was by value; this is not correct.  There is no cheap
 * way to determine function argument length etc.; one must simply pay
 * the price of catalog lookups.
 */
struct fp_info {
    Oid		funcid;
    int			nargs;
    bool		argbyval[MAXFMGRARGS];
    int32		arglen[MAXFMGRARGS];	/* signed (for varlena) */
    bool		retbyval;
    int32		retlen;			/* signed (for varlena) */
    TransactionId	xid;
    CommandId		cid;
};

/*
 * We implement one-back caching here.  If we need to do more, we can.
 * Most routines in tight loops (like PQfswrite -> F_LOWRITE) will do
 * the same thing repeatedly.
 */
static struct fp_info last_fp = { InvalidOid };

/*
 * valid_fp_info
 *
 * RETURNS:
 *	1 if the state in 'fip' is valid
 *	0 otherwise
 *
 * "valid" means:
 * The saved state was either uninitialized, for another function,
 * or from a previous command.  (Commands can do updates, which
 * may invalidate catalog entries for subsequent commands.  This
 * is overly pessimistic but since there is no smarter invalidation
 * scheme...).
 */
static int
valid_fp_info(Oid func_id, struct fp_info *fip)
{
    Assert(OidIsValid(func_id));
    Assert(fip != (struct fp_info *) NULL);
    
    return(OidIsValid(fip->funcid) &&
	   oideq(func_id, fip->funcid) &&
	   TransactionIdIsCurrentTransactionId(fip->xid) &&
	   CommandIdIsCurrentCommandId(fip->cid));
}

/*
 * update_fp_info
 *
 * Performs catalog lookups to load a struct fp_info 'fip' for the
 * function 'func_id'.
 *
 * RETURNS:
 *	The correct information in 'fip'.  Sets 'fip->funcid' to
 *	InvalidOid if an exception occurs.
 */
static void
update_fp_info(Oid func_id, struct fp_info *fip)
{
    Oid		*argtypes;	/* an oid8 */
    Oid		rettype;
    HeapTuple		func_htp, type_htp;
    TypeTupleForm	tp;
    Form_pg_proc	pp;
    int			i;
    
    Assert(OidIsValid(func_id));
    Assert(fip != (struct fp_info *) NULL);

    /*
     * Since the validity of this structure is determined by whether
     * the funcid is OK, we clear the funcid here.  It must not be
     * set to the correct value until we are about to return with
     * a good struct fp_info, since we can be interrupted (i.e., with
     * an elog(WARN, ...)) at any time.
     */
    memset((char *) fip, 0, (int) sizeof(struct fp_info));
    fip->funcid = InvalidOid;

    func_htp = SearchSysCacheTuple(PROOID, ObjectIdGetDatum(func_id),
				   0,0,0);
    if (!HeapTupleIsValid(func_htp)) {
	elog(WARN, "update_fp_info: cache lookup for function %d failed",
	     func_id);
    }
    pp = (Form_pg_proc) GETSTRUCT(func_htp);
    fip->nargs = pp->pronargs;
    rettype = pp->prorettype;
    argtypes = pp->proargtypes;

    for (i = 0; i < fip->nargs; ++i) {
	if (OidIsValid(argtypes[i])) {
	    type_htp = SearchSysCacheTuple(TYPOID, 
					   ObjectIdGetDatum(argtypes[i]),
					   0,0,0);
	    if (!HeapTupleIsValid(type_htp)) {
		elog(WARN, "update_fp_info: bad argument type %d for %d",
		     argtypes[i], func_id);
	    }
	    tp = (TypeTupleForm) GETSTRUCT(type_htp);
	    fip->argbyval[i] = tp->typbyval;
	    fip->arglen[i] = tp->typlen;
	} /* else it had better be VAR_LENGTH_ARG */
    }

    if (OidIsValid(rettype)) {
	type_htp = SearchSysCacheTuple(TYPOID, ObjectIdGetDatum(rettype),
				       0,0,0);
	if (!HeapTupleIsValid(type_htp)) {
	    elog(WARN, "update_fp_info: bad return type %d for %d",
		 rettype, func_id);
	}
	tp = (TypeTupleForm) GETSTRUCT(type_htp);
	fip->retbyval = tp->typbyval;
	fip->retlen = tp->typlen;
    } /* else it had better by VAR_LENGTH_RESULT */

    fip->xid = GetCurrentTransactionId();
    fip->cid = GetCurrentCommandId();

    /*
     * This must be last!
     */
    fip->funcid = func_id;
}
	

/*
 * HandleFunctionRequest
 *
 * Server side of PQfn (fastpath function calls from the frontend).
 * This corresponds to the libpq protocol symbol "F".
 *
 * RETURNS:
 *	nothing of significance.
 *	All errors result in elog(WARN,...).
 */
int
HandleFunctionRequest()
{
    Oid		fid;
    int		argsize;
    int		nargs;
    char	*arg[8];
    char	*retval;
    int			i;
    uint32		palloced;
    char		*p;
    struct fp_info	*fip;

    fid = (Oid) pq_getint(4);	/* function oid */
    nargs = pq_getint(4);	/* # of arguments */

    /*
     * This is where the one-back caching is done.
     * If you want to save more state, make this a loop around an array.
     */
    fip = &last_fp;
    if (!valid_fp_info(fid, fip)) {
	update_fp_info(fid, fip);
    }

    if (fip->nargs != nargs) {
	elog(WARN, "HandleFunctionRequest: actual arguments (%d) != registered arguments (%d)",
	     nargs, fip->nargs);
    }

    /*
     *  Copy arguments into arg vector.  If we palloc() an argument, we need
     *  to remember, so that we pfree() it after the call.
     */
    palloced = 0x0;
    for (i = 0; i < 8; ++i) {
	if (i >= nargs) {
	    arg[i] = (char *) NULL;
	} else {
	    argsize = pq_getint(4);
	    
	    Assert(argsize > 0);
	    if (fip->argbyval[i]) {		/* by-value */
		Assert(argsize <= 4);
		arg[i] = (char *) pq_getint(argsize);
	    } else {			/* by-reference ... */
		if (fip->arglen[i] < 0) {		/* ... varlena */
		    if (!(p = palloc(argsize + VARHDRSZ))) {
			elog(WARN, "HandleFunctionRequest: palloc failed");
		    }
		    VARSIZE(p) = argsize + VARHDRSZ;
		    pq_getnchar(VARDATA(p), 0, argsize);
		} else {				/* ... fixed */
			/* XXX cross our fingers and trust "argsize" */
			if (!(p = palloc(argsize))) {
			    elog(WARN, "HandleFunctionRequest: palloc failed");
			}
			pq_getnchar(p, 0, argsize);
		    }
		palloced |= (1 << i);
		arg[i] = p;
	    }
	}
    }

#ifndef NO_FASTPATH
    retval = fmgr(fid,
		  arg[0], arg[1], arg[2], arg[3],
		  arg[4], arg[5], arg[6], arg[7]);

#else
    retval = NULL;
#endif /* NO_FASTPATH */

    /* free palloc'ed arguments */
    for (i = 0; i < nargs; ++i) {
	if (palloced & (1 << i))
	    pfree(arg[i]);
    }

    /*
     *  If this is an ordinary query (not a retrieve portal p ...), then
     *  we return the data to the user.  If the return value was palloc'ed,
     *  then it must also be freed.
     */
#ifndef NO_FASTPATH
    SendFunctionResult(fid, retval, fip->retbyval, fip->retlen);
#else
    SendFunctionResult(fid, retval, fip->retbyval, 0);
#endif /* NO_FASTPATH */

    if (!fip->retbyval)
	pfree(retval);

    
    
    return(0);
}
